This application claims the benefit of Korean Patent Application No. 2000-74796 filed on Dec. 8, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a four-axial driving actuator for an optical pickup, and more particularly, to a four-axial driving actuator for an optical pickup in which the winding starting ports of a focusing coil, tracking coil, and tilt coil are separate from one another and the winding end ports thereof are combined as a common ground so that moving characteristics of a bobbin are improved.
2. Description of the Related Art
In general, an optical pickup is a device employed in an optical recording/reproduction apparatus to record information on and/or reproduce information from a disc mounted as a recording medium on a turn table in a non-contact manner while moving in the radial direction of the disc. The optical pickup includes an objective lens that focuses a beam emitted from a light beam source to form a beam spot on the disc, and an actuator that controls the objective lens in the track direction, focus direction, and tilt direction such that the beam spot from the objective lens can be accurately focused on an intended position in the optical disc.
An actuator for an optical pickup is classified as either a hinged type, plate spring type, wire type, or an axial sliding type according to its bobbin support structure. The wire type is advantageous in that current can be supplied to a driving coil using a wire supporting the bobbin.
Referring to FIG. 1, a conventional wire-type optical pickup actuator includes a base 100, a holder 103 fixed on the base 100, a bobbin 107 to which the objective lens 105 is fixed, wires connected between the bobbin 107 and the holder 103, and a magnetic driving unit driving the bobbin 107 in the track, focus or tilt direction.
The magnetic driving unit includes a first magnet 110 and a second magnet 112, each facing a corresponding first and second magnet 110 and 112, respectively, with the bobbin 107 therebetween, an outer yoke 115 which is mounted on the base 100 and to which the first magnet 110 is fixed, an inner yoke 117 mounted on the base 100 facing one of the first magnets 110 to guide the bobbin 107, a focusing coil 120 wound around the outer wall of the bobbin 107, a tracking coil 122 wound at the side wall of the bobbin 107 facing one of the first magnets 110, and portions of a tilt coil 125 wound at each of the side walls of the bobbin 107 facing the second magnets 112.
FIG. 2 is a front view of the bobbin 107 of FIG. 1. Referring to FIGS. 1 and 2, the wires includes focusing coil wires 130 connecting the focusing coil 120 to the winding starting port 127 and the winding end port 129 thereof, tracking coil wires 135 connecting the tracking coil 122 to the winding starting port 132 and the winding end port 133 thereof, and tilt coil wires 140 connecting the tilt coil 125 to the winding starting port 137 and the winding end port 139 thereof. The wires 130, 135, and 140 serve as a support for the bobbin 107 driven by the magnetic driving unit by connecting the bobbin 107 to the holder 103, as well as serving as electric wires through which current is applied to the focusing coil 120, the tracking coil 122, and the tilt coil 125.
A general actuator includes four wires including a pair of focus coil spring wires 130 and a pair of tracking coil spring wires 135. In addition, tilt coil spring wires may be elastically connected between the bobbin 107 and the holder 103 to support the bobbin 107, further elastically biasing the bobbin 107 toward the holder 103. As a result, motion of the bobbin 107 is further limited. Taking into account this problem, the tilt coil wires 140 are arranged loosely over the holder 103 and connected to the rear wall of the holder 103, as shown in FIG. 1.
The bobbin 107 is driven by the magnetic driving unit having the configuration above in four axial directions, i.e., in the focus direction A, track direction B, tangential tilt direction C, and radial tilt direction D. FIG. 3 shows a voltage apply circuit for each of the coils. Although the circuit for only the focusing coil 120 is illustrated here, the tracking coil 122 and the tilt coil 125 have the same structure.
Referring to FIG. 3, the focus coil circuit includes an input generator 145, comparators 147, the winding starting port 127 of the focusing coil 120 to which a driving voltage is applied from one of the comparators 147, and the winding end port 129 through which a current flowing through the focusing coil 120 is output. This circuit structure is also applied to both the tracking coil 122 and the tilt coil 125, and thus a total six wires are needed for the actuator.
In the conventional four-axial driving actuator having the configuration above, the six wires are complexly arranged, and moving characteristics of the bobbin 107 are affected by the length or position of the tilt coils 125, causing a secondary resonance or a rolling of the bobbin 107 to occur in driving the bobbin 107.
To solve the above and other problems, it is an object of the present invention to provide a four-axial driving actuator for an optical pickup, in which the winding starting ports of a focusing coil, a tracking coil, and a tilt coil are separate from one another and the winding end ports thereof are combined as a common ground so that moving characteristics of a bobbin are improved.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing objects of the present invention are achieved by providing a four-axial driving actuator for an optical pickup, comprising: a base; a holder fixed on the base; a bobbin to which an objective lens is fixed; spring wires connected between the bobbin and the holder; and a magnetic driving unit driving the bobbin in the focus, track, or tilt direction with a focusing coil, a tracking coil, and a tilt coil, wherein the magnetic driving unit comprises a circuit unit including winding starting ports for the focusing coil, tracking coil, and tilt coil, and a common ground port at which winding end ports for the focusing coil, tracking coil, and tilt coil are grounded, and the circuit unit applies a voltage to the focusing coil, tracking coil, and tilt coil.
The magnetic driving unit may comprise a first magnet and a second magnet, each facing a corresponding first and second magnet, respectively, with the bobbin therebetween; an outer yoke which is mounted on the base and to which a first magnet is fixed; and an inner yoke mounted on the base facing the first magnet to guide the bobbin, wherein the focusing coil is wound around the outer wall of the bobbin, the tracking coil is wound at the side wall of the bobbin facing the first magnet, and the tilt coil is wound at the side wall of the bobbin facing the second magnet. It is to be noted that the positioning of the magnets, and also the number of magnets used shall not be limited by this description, but may vary such that the desired effect is obtained.
The circuit unit may also comprise an input generator to generate a voltage to be applied to the focusing coil, tracking coil, or tilt coil; and a filter that removes a high-frequency noise component from the voltage applied from the input generator to supply a noise-free voltage to the focusing coil, tracking coil, or tilt coil. In the alternative, a separate input generator may be provided for each of the focusing coil, tracking coil, and tilt coil.